This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. The basis for how the small GTPase Arf1 recruits protein trafficking cargo adaptors to membranes remains largely unknown. Although the structure of Arf1 has been known for years, we know very little about how Arf proteins orient cargo adaptors or vesicle coats with respect to membranes or membrane-bound cargo proteins. Exomer is a temporally regulated Arf1-dependent oligomeric cargo adaptor. Interestingly, oligomerization of exomer is required for its Arf1-dependent membrane binding. We plan to characterize the architecture of the exomer complex and how it binds to Arf1, in order to elucidate the role of Arf1-binding in cargo adapter membrane association. SAXS experiments performed at CHESS will be used for determining the oligomeric state of exomer, and for positioning the subunits within the complex. Furthermore, SAXS analysis of an Arf1-exomer complex will indicate the position of Arf1-binding on the exomer oligomer.